1. Field of the Invention
The present invention relates in general to an ink package having a simple structure which prevents deterioration of a degree of deaeration of ink accommodated in the ink package and evaporation of an aqueous component of the ink, the ink in the ink package being given positive pressure in the simple structure. The present invention also relates to a method of producing such an ink package.
2. Discussion of Related Art
As disclosed in JP-A-11-129489 (FIG. 1, in particular), there is known an ink bag in which ink is fluid-tightly accommodated and which is used for an ink-jet recording apparatus. To the opening of the ink bag, there is fixed a tubular member into which an elastic sealing member is fitted for inhibiting communication between an exterior and an interior of the ink bag. The ink bag is accommodated in and attached to a cartridge casing such that one of opposite ends of the tubular member is exposed to an exterior of the casing. The cartridge casing in which the ink bag is accommodated is installed on the ink-jet recording apparatus. Upon installation of the cartridge casing on the recording apparatus, an ink-extracting needle of the apparatus pierces the elastic sealing member fitted in the tubular member, so that the ink in the ink bag is supplied, via a tube connected to the ink-extracting needle, to the ink-jet printing head through which the ink is ejected to a recording medium.
The ink used for the ink-jet recording apparatus is manufactured by a process including a step of dissolving an ink material in a solvent, and a step of filtering a solution of the ink material. Where the ink as manufactured by this process is accommodated in the ink bag for use on the ink-jet recording apparatus, various kinds of gases such as nitrogen, oxygen and carbon dioxide that are dissolved in the ink are introduced together with the ink into the ink-jet printing head, causing bubbles that may prevent the ink-jet printing head from smoothly ejecting droplets of the ink, giving rise to a risk of a poor ink-ejecting performance of the head. To avoid this drawback, it has been practiced to carry out a deaerating or degassing treatment of the ink, so as to reduce the amounts of the dissolved gases before the ink is accommodated in the ink bag.
When the ink bag in which the thus deaerated or degassed ink is accommodated is transported, or stored for a long time before its use, oxygen and other gases in the air may be dissolved in the ink. JP-B2-3-61592 (column 4, lines 4-7, and FIG. 1, in particular) discloses a technique to prevent the dissolution of such gases in the ink. According to this technique, an ink bag filled with the degassed ink is accommodated in a suitable ink-bag casing, and this ink-bag casing is placed in a vacuum chamber the pressure of which is adjusted to a reduced pressure lower than the atmospheric level, and is fluid-tightly enclosed or accommodated within a sealing wrapper or container such as a plastic or rubber bag or a metallic can or box, so that the casing is kept under the reduced pressure in the evacuated container, during transportation or storage.
JP-A-59-59457 or its corresponding U.S. Pat. No. 4,558,326 discloses a technique of conducting a so-called “purging operation” for discharging or getting rid of, from the ink-jet printing head, bubbles and poor-quality ink whose viscosity has been increased. In the disclosed technique, there is supplied positively pressurized air between an ink bag in which the ink is accommodated and a rigid cartridge casing in which the ink bag is accommodated, so that the ink in the ink bag is pressurized. The pressurized ink is supplied to the ink-jet printing head.
Where the ink bag filled with the deaerated ink is accommodated in the ink-bag casing as disclosed in JP-B-3-61592, the ink-bag casing enclosed in the evacuated container is kept in a substantially fluid-tightly or hermetically sealed state, so that a space between the ink-bag casing and the container is easily kept exposed to the reduced pressure lower than the atmospheric pressure. However, it is rather difficult to evacuate a space between the ink bag and the ink-bag casing to the reduced pressure. Accordingly, the air existing in the space between the ink bag and the ink-bag casing is inevitably dissolved in the ink in the ink bag, undesirably deteriorating the deaeration degree of the ink.
For satisfying a recent demand for increasing the volume of the ink to be accommodated in the ink bag, it is necessary to increase the size of the cartridge casing in which the ink bag is accommodated. Since the ink bag generally has a flattened shape as disclosed in JP-A-11-129489, the rigid cartridge casing for accommodating the ink bag also has a flattened shape having walls of a large surface area. If the cartridge casing accommodated in the container is exposed to the reduced pressure, the cartridge casing having the flattened shape is undesirably deformed at the walls of the large surface area due to the exposure to the reduced pressure. To avoid this, the cartridge casing needs to be manufactured such that the cartridge casing exhibits a relatively high degree of mechanical strength. However, this undesirably pushes up the cost of the manufacture of the cartridge casing.
Where the positively pressurized air is supplied between the ink bag and the rigid cartridge casing as disclosed in JP-A-59-59457, it is required to fluid-tightly seal, with high stability, connecting portions of components of the rigid cartridge casing to prevent a leakage flow of the positively pressurized air therefrom for supplying, to the ink-jet printing head, the ink under predetermined pressure. Accordingly, the cost of manufacture of the cartridge casing is inevitably increased.